The present invention relates to an airbag for an airbag device installed in an vehicle, such as automobile and aircraft, and more particularly, to an airbag for preventing gas leakage at a joint of panels of the airbag.
Conventionally, an airbag comprising a plurality of panels which are sewn together to form an envelope-like configuration has been employed as a driver""s airbag, a front passenger""s airbag, a rear passenger""s airbag, or a side airbag installed in an automobile, or an airbag installed in an aircraft. The airbag is inflated with gas from an inflator.
In an airbag, such as a side airbag for protecting an occupant""s head as a curtain-type airbag and a side airbag for protecting an occupant during roll-over, an inner pressure thereof has to be kept high for a long period of time. Thus, it is required to surely prevent a gas leakage at a sewn portion. However, when the airbag is inflated, weaving yarns or threads are strongly pulled by a sewing yarn or thread to thereby widen interstices or make holes along the sewing yarn penetrating the panels of the airbag. The holes allow gas to leak therethrough.
To prevent the gas leakage from the sewn portion of the panels of the airbag, conventionally, as shown in FIGS. 4(a) and 4(b), silicone tapes 4 are attached to cover the sewn portion 3 of the panels 1, 2 along the peripheral edges thereof.
In the conventional airbag shown in FIGS. 4(a) and 4(b), when the gas pressure in the airbag is high, as shown in FIG. 4(b), the gas may leak from a space between the panels 1, 2.
In view of the conventional airbag, the present invention has been made, and an object of the present invention is to provide an airbag which can securely prevent a gas leakage at a joining portion of panels of the airbag.
Another object of the invention is to provide an airbag as stated above, which has a quite high bonding strength between the panels.
Further objects and advantages of the invention will be apparent from the following description of the invention.
An airbag of the present invention comprises a first main panel and a second main panel which are joined to each other at a joining portion to form a chamber, which is defined by the first and second main panels and the joining portion. The airbag is inflatable when gas is supplied into the chamber.
In the invention, the airbag further includes a first inner panel and a second inner panel interposed between the first and second main panels over the joining portion. Namely, the first inner panel is bonded to the first main panel and the second inner panel is bonded to the second main panel. The first inner panel and the second inner panel are joined to each other at a position away from the inner edge of the chamber or the joining portion.
According to the airbag, since no sewing yarn or thread penetrates the first and second main panels, there is no possibility of widening interstices or making holes of the main panels. This means that gas leakage through the holes does not occur.
In the present invention, since the first inner panel is bonded to the first main panel and the second inner panel is bonded to the second main panel, the bonding-strength between each inner panel and the corresponding main panel is sufficiently high. Also, each inner panel is bonded to the corresponding main panel over the entire surface of the inner panel, thereby making the bonding strength significantly high.
The inner panels may be joined strongly to each other, for example, by sewing. On the other hand, the first inner panel and the second inner panel may be formed by folding a piece of panel. In this case, the strength between the first inner panel and the second inner panel is significantly high.
As apparent from the above, the present invention can provide the airbag having significantly high bonding strength between the main panels.
In case the peripheral portions of the main panels are joined to each other, it is preferable that the inner panels are positioned away from the peripheral edges of the main panels for a predetermined distance, and the main panels are bonded to each other between the inner panels and the outer edges of the main panels. Even when the gas pressure in the airbag is high, the gas leakage through a space between the first main panel and the second main panel can be prevented.
In the present invention, the first main panel and the second main panel may be joined to each other not only along the peripheries of the main panels, but also about the center of the chamber. At the joint about the center of the chamber, two inner panels, preferably joined to each other by sewing, may be used.